1. Field of the Invention
The present invention relates to a numerical control unit capable of changing the feed speed by an override.
2. Description of the Related Art
JP 2010-9094 A discloses a technology that superimposes the amount of movement of high speed cycle machining that repeatedly performs the same operation and an NC program. The high speed cycle machining is a function capable of executing distributed data stored in a variable area at high speed. High speed cycle machining data stored in the variable area includes a header and distributed data. FIG. 1 illustrates an example of the header and distributed data. FIG. 2 illustrates an example of distributed data concerning an axis.
High speed cycle machining data can be invoked and executed by an NC program command.
As described above, the technology disclosed by JP 2010-9094 A is used, as illustrated in FIG. 3, to superimpose a repeated operation by high speed cycle machining and any operation by an NC program on top of each other. Accordingly, the high speed cycle machining executes high speed cycle machining data for one cycle repeatedly and therefore, the capacity of high speed cycle machining data can be reduced.
However, when a smooth speed change is made to reduce machine shock or a machining error, one of the following two techniques is needed.    (1) Technique to create and execute high speed cycle machining data in consideration of acceleration/deceleration    (2) Technique to change an override by a tiny amount each time using a ladder program
These are techniques needed to avoid acceleration/deceleration after interpolation so that high speed cycle machining can realize a fast response.
FIG. 4 illustrates an example of high speed cycle machining data in consideration of acceleration/deceleration. While a constant speed portion repeatedly executes high speed cycle machining data for one cycle, an acceleration portion and a deceleration portion need to execute dedicated high speed cycle machining data. If the feed speed is different in a machining process such as rough machining or finishing machining, it is necessary to execute high speed cycle machining data of the acceleration portion/constant speed portion/deceleration portion for each machining process. Therefore, a problem of an increased capacity of high speed cycle machining data and also an increased load of creating high speed cycle machining data is posed.
The override is a function capable of changing the feed speed by specifying a multiplying factor (%) of the commanded speed of a program by an input signal. An actual override to obtain an actual feed speed by multiplying the commanded speed thereby is calculated from the override specified by the input signal and the feed speed is calculated by multiplying the commanded speed by the actual override. When accelerated/decelerated by changing the override, the capacity of high speed cycle machining data can be reduced because high speed cycle machining data for acceleration/deceleration is not needed and also the load of creating highspeed cycle machining data can be reduced.
FIG. 5 illustrates an example in which high speed cycle machining data in consideration of acceleration/deceleration is executed and an example in which the override is changed and the feed speed is changed by the same amount each time. The update cycle of override is the signal input cycle, for example, 4 msec and the override is conventionally set directly as the actual override. Accordingly, the cycle in which the actual override changes is longer than the interpolation cycle, for example, 1 msec. Therefore, there is a problem of taking a longer time for acceleration/deceleration when the override is changed compared with a case when high speed cycle machining data in consideration of acceleration/deceleration is used.
A case when the override is changed by a tiny amount each time will be examined. The override is not limited to high speed cycle machining and can also be used for machining by the NC program command. For example, if the feed speed is fast in a water-jet cutting machine, as illustrated in FIG. 6, delay of water flow response arises. In such a case, the override is conventionally updated by a tiny amount each time using a ladder program and the override is directly set as an actual override. Accordingly, the delay of water flow response can be reduced by making a speed such that the change time of speed becomes longer. The speed change using the override can be made independently of acceleration/deceleration after the interpolation and therefore, gradual acceleration/deceleration can be implemented. However, a problem of the load of creating a ladder program is posed.
JP 2012-32960 A discloses a technology that, when a special command to make a speed change such as an emergency stop or an override is input, changes the length of the set unit time to a length in accordance with a speed change of a moving target instructed by the special command to calculate the amount of movement per set unit time after the change. However, the technology disclosed by JP 2012-32960 A is a technology that recalculates the amount of movement by a simple technique after a special command to make a speed change is input to enhance responsiveness of the operation thereof. The technology cannot be applied when a gradual speed change is made by changing the override by a tiny amount each time.